In positron-emission tomography, the distribution of a radioactive marker substance which has previously been introduced into the organism of an examination object is tracked in the body in order in this way to attain mainly functional images and data about the biochemical and physiological processes taking place. The time resolution of positron-emission tomography is rather poor in comparison to other imaging methods. In the case of positron-emission tomography, the images are typically recorded in different sections, which are referred to as “bed positions”, and each require a recording time in the range from 2 to 5 minutes. In comparison to these long recording times, a range of movement processes take place in the body, for example, breathing or the heart rhythm, with shorter time constants than those which are relevant for the recording of the individual “bed positions”.
Other imaging methods, in particular, anatomical imaging methods, whose data can be used to complete the validity of the positron-emission tomography data, for example relating to the glucose metabolism, have higher time resolution. For example, when using computed tomography, entire body recordings are carried out with measurement times in the range from a few seconds up to about two minutes.
Since the area of interest of the examination object is in motion during one “bed position”, the recorded positron-emission data represents a time average over the body movement. This necessarily leads to a considerable reduction in the image quality of the images obtained from positron-emission measurement information.
There are admittedly approaches for providing schemes for recording and reconstruction of positron-emission measurement information in order to obtain four-dimensional positron-emission data records, that is to say data resolved in time, but these have so far been inadequate to make it possible to carry out or to satisfactorily achieve fusion or superimposition with anatomical data from an anatomical imaging method such as computed tomography, whose data is not isocentric with respect to the positron-emission data.
For example, attempts have been made to access triggers resulting from the heart rhythm or breathing during positron-emission data recording. These triggers detect peaks in the heart rhythm or in the breathing cycle, and these are used to reconstruct the image data taking account of the time delay with respect to the peak, as a time-resolving parameter. However, one problem that arises in this case is that the respective cycles have variable time durations, for example, because of physiological influences such as stress, arrhythmia, coughing or the like. In consequence, the time averaging process becomes extremely complicated. Furthermore, breathing-related triggers are not very reliable for various reasons, for example, with regard to the breathing depth, so that a peak or the starting point of a cycle is frequently not recognized.